Macrurobolus, Pimvichai & Enghoff & Backeljau, 2022

Pimvichai, Piyatida, Enghoff, Henrik & Backeljau, Thierry, 2022, Redescription of the giant Southeast Asian millipede Spirobolus macrurus Pocock, 1893 and its assignment to the new genus Macrurobolus gen. nov. (Diplopoda, Spirobolida, Pachybolidae), ZooKeys 1087, pp. 1-18 : 1

Genus Macrurobolus gen. nov.

Figures 1 , 2 , 3 , 4 , 5

Diagnosis.

A genus of Pachybolidae characterised by the following combination of characters: preanal ring with long process protruding beyond anal valves; the anterior gonopod telopodite distally abruptly narrowed, forming an extremely long, slender, elevated process curved caudad.

Etymology.

The generic name is a combination of the name of the type species and “-bolus”, the ending of many pachybolid genus names.

Type species.

Macrurobolus macrurus (Pocock, 1893) comb. nov.

Spirobolus macrurus Pocock 1893: 396.

Tonkinbolus macrurus : Hoffman 1962: 773.

Atopochetus macrurus : Pimvichai et al. 2018: 174.

Macrurobolus macrurus

(Pocock, 1893), comb. nov.

The original description was based exclusively on a female from “Kawkareet” (Tenasserim), Myanmar (see Distribution section for information on this locality). Pocock (1893) described the female external morphology and mentioned that this species differed from Spirobolus caudulanus [= Atopochetus caudulanus (Karsch, 1881)] and Spirobolus moulmeinensis [= Atopochetus moulmeinensis (Pocock, 1893)] by having a "much longer and thinner tail".

Material studied.

Thailand, 1 ♂, 3 ♀♀; Tak Province, Mae Sot District, Wat Tham Inthanin ; 16°45'59"N, 98°40'21"E; 660 m a.s.l.; 27 July 2016; P. Pimvichai, T. Backeljau and P. Prasankok leg. (CUMZ) . • Myanmar, 1 ♂; Meetan; Fea; "ex typ."; NHMD 621698 .

Description of Thai specimens.

Adult male with 51 podous rings, no apodous rings. Length ca 11 cm, diameter ca 9.0 mm. Adult females with 48-51 podous rings, no apodous rings. Length ca 10-11 cm, diameter ca 10.0-10.4 mm.

Head capsule smooth, area below antennal sockets with wrinkles (Fig. 2A ). Occipital furrow extending down between, but not beyond eyes; clypeal furrow reaching level of antennal sockets. Area below antennal sockets and eyes impressed, forming part of antennal furrow. Incisura lateralis open. 2+2 labral teeth, a row of labral setae, 1+1 supralabral setae (mentioned as "the labral region furnished with 4 punctures" by Pocock 1893: 401). Diameter of eyes ca half of interocular space; 9 vertical rows of ommatidia, 8 horizontal rows, 53-55 ommatidia per eye. Antennae short, not reaching beyond collum when stretched back, accommodated in a shallow furrow composed of a horizontal segment in the head capsule and a vertical segment in the mandibular cardo and stipes. Antennomere lengths 2> 3 = 5> 4> 6> 1> 7; antennomere 1 glabrous, 2 and 3 with some ventral setae, 4, 5 and 6 densely setose; 4 apical sensilla. Mandibles: stipes (Mst) broad at base, apically gradually narrowed. Gnathochilarium (Fig. 2B ): each stipes (Gst) with 3 apical setae; each lamella lingualis with 2 setae, one behind the other. Basal part of mentum (Me) transversely wrinkled; basal part of stipites longitudinally wrinkled.

Collum smooth, with a marginal furrow along lateral part of anterior margin; lateral lobes narrowly rounded, extending as far ventrad as the ventral margin of body ring 2.

Body rings 2-5 ventrally concave, hence with distinct ventrolateral “corners”. Body rings very smooth, parallel-sided in dorsal view. Prozona smooth. ‘Tergo-pleural’ suture visible on pro- and mesozona; mesozona ventrally with fine oblique striae, dorsally punctate; metazona ventrally with fine longitudinal striae, otherwise smooth. “Pleural” parts of rings with fine oblique striae. Sterna transversely striate. Ozopores from ring 6, situated in mesozona, ca 1/2 pore diameter in front of metazona (mentioned as "the repugnatorial pores situated in front of the transverse sulcus" by Pocock 1893: 401).

Telson smooth; preanal ring with slightly concave dorsal profile, with thick and long process protruding beyond anal valves (Fig. 2C ). Anal valves (Av) impressed submarginally (Fig. 2D ); margins hence distinctly protruding, liplike. Subanal scale (Sub) broadly triangular.

Legs (Fig. 2E ): length of midbody legs 72-77% of body diameter in males, 54-56% of body diameter in females. Prefemur basally constricted, tarsus longer than other podomeres. First and second legs with 2 or 3 prefemoral, 2 or 3 femoral, 2 or 3 postfemoral, and 2-4 tibial setae, and 4 or 5 ventral and 1 dorsal apical setae on tarsi, numbers of setae reaching constancy from pair 3: each leg podomere from coxa to tibia with 1 seta; tarsi with 2 ventral apical and 1 dorsal apical seta, the apical ventral seta larger than the more basal one. Claw very slender, more than half as long as tarsus.

Colour. Living animal reddish brown except for grey pro- and mesozona (Fig. 4 ).

Male sexual characters. Tarsus from third to before the last 4 body rings with large ventral soft pad occupying entire ventral surface. Body ring 7 entirely fused ventrally, no trace of a suture. Tip of anterior gonopods visible when the animal is stretched out (not when it is rolled up).

Anterior gonopods (Fig. 3A, B, D, E ) with triangular mesal sternal process, not reaching so far as the tip of coxae, apical margin bilobed, with basal longitudinal triangular ridge in posterior view. Coxa oval, apically gradually narrowed, rounded, projecting slightly beyond sternal process. Telopodite apically far overreaching coxa, distally abruptly narrowed, forming an extremely long, slender, elevated process curved caudad.

Posterior gonopods (Fig. 3C, F, H-I ) strongly curved mesad, laterally with a massive ridge; with efferent canal ( Enghoff 2011) running along mesal margin terminating in slender, pointed meso-distad process, covered with fine hairlike spinules (Fig. 3L ); tip of posterior gonopod concave, apically ending in a rounded lobe (Fig. 3I , showed serrated margin, dorsally covered with short spines); with spiny lamellae mesally near tip.

Female vulvae (Fig. 3G ). Valves prominent, of equal size; basally with open space between free margins.

DNA barcode.

The GenBank accession number of the COI barcode of the Thai specimen is MZ905519 (voucher code CUMZ-D00147).

Ecology

. Found under leaf litter.

Notes on the male from Meetan, Myanmar.

This specimen is labelled as "ex typ" in the NHMD collection and was, like the female type specimen, collected by Fea. It agrees with the Thai male in all characters, including all details of gonopod shape, with the following exceptions: Colour after> 100 years in alcohol is faded, but there is still a clear contrast between greyish pro- and mesozone and reddish-brown metazona. Size: length ca 8 cm, diameter 6.7 mm, 50 podous rings, no apodous rings in front of telson. Head capsule smooth. 11 vertical rows of ommatidia, of which 3 are very incomplete, 7 horizontal rows, 47 ommatidia per eye. Antennomeres 2-4 with some ventral setae, 5 and 6 densely setose. Gnathochilarium not dissected.

Distribution.

Tak Province, Thailand; Kawkareet (Tenasserim) and Meetan, Myanmar (Fig. 5 ). The names Kawkareet and Meetan do not appear on maps available to us. However, Brandis (2002: 1312) mentioned "Meetan (= Mitan Chaung (= river) 15°59'00"N 98°24'00"E at the south-west slope of the Dawna mountain", whereas Randall and Page (2012: 344) located Meetan at " 16.555556°N, 98.24°E (coordinates estimated)". Annandale (1911: 118) stated that Kawkareet refers to Kawkareik and remarked in a footnote that "This locality [i.e. Kawkareik] is often referred to in zoological literature as Kawkareet or Kawkarit, or even Kokarit". Finally, Likhitrakarn et al. (2017) located Kawkareet (= Kawkareik) at 16°33'20"N, 98°14'24"E and Meetan (= Mi Tan) at 16°00'12"N, 98°23'25"E.

Figures

Figure 1. Phylogenetic relationships of pachybolid and several other spirobolidan millipede species based on maximum likelihood analysis (ML) of a 660 bp COI gene fragment. Numbers at nodes indicate branch support based on bootstrapping (ML) / posterior probabilities (BI) / bootstrapping (NJ). Scale bar: 0.3 substitutions / site. indicates branches with <50 % ML and NJ bootstrap support or <0.95 posterior probability, - indicates non-supported branches. The coloured areas mark the Pseudospirobolellidae (minus Benoitolus) (purple), Trigoniulinae (red), and non-trigoniuline Pachybolidae (plus Benoitolus) (yellow).

Figure 2. External morphology of a male Macrurobolus macrurus comb. nov. from Wat Tham Inthanin, Thailand, CUMZ-D 00147 - 1 A head, frontal view B gnathochilarium, ventral view C posterior end, lateral view D posterior end, latero-ventral view E midbody leg, latero-ventral view. Av = anal valves; Gst = gnathochilarial stipes; Me = mentum; Mst = mandibular stipes; Sub = subanal scale.

Figure 3. Male (A-F, H-L) and female (G) genital parts of Macrurobolus macrurus comb. nov. (specimens from Wat Tham Inthanin, Thailand, CUMZ-D 00147 - 1) A anterior gonopod, anterior view B anterior gonopod, posterior view C right posterior gonopod, posterior-mesal view D anterior gonopod, anterior view E anterior gonopod, posterior view F right posterior gonopod, posterior-mesal view G left female vulva, posterior mesal view H-L SEM H left posterior gonopod, posterior-mesal view I tip of posterior gonopod, mesal view J apical part of posterior gonopod, mesal view K spiny lamellae near tip of posterior gonopod, mesal view L meso-distad process of posterior gonopod, posterior-mesal view. at = anterior gonopod telopodite; av = anterior valve; cx = coxa; pt = posterior gonopod telopodite; pv = posterior valve; st = sternum.

Figure 4. Live female Macrurobolus macrurus comb. nov. from Wat Tham Inthanin, Thailand (CUMZ-D 00147 - 3).

Figure 5. Distribution of Macrurobolus macrurus comb. nov.